# What is coincidence: Definition and 56 Discussions

A coincidence is a remarkable concurrence of events or circumstances that have no apparent causal connection with one another. The perception of remarkable coincidences may lead to supernatural, occult, or paranormal claims, or it may lead to belief in fatalism, which is a doctrine that events will happen in the exact manner of a predetermined plan. In general, the perception of coincidence, for lack of more sophisticated explanations, can serve as a link to folk psychology and philosophy.From a statistical perspective, coincidences are inevitable and often less remarkable than they may appear intuitively. Usually, coincidences are chance events with underestimated probability. An example is the birthday problem, which shows that the probability of two persons having the same birthday already exceeds 50% in a group of only 23 persons.

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1. ### I Unlocking the Potential of Back-to-Back Photons: an Experiment

In some cases, photons can be produced in "back to back" (BTB) conditions. For example, electron-positron annihilation produces two photons, each at 0.511 MeV, with equal and opposite momentum. Or pretty close, up to the original velocities of the electron and positron. Start with a source of...
2. ### Can MCNP solve the geometric coincidence issue with a semi-cylinder and cuboid?

How do we solve the geometric coincidence problem? I need a semi-cylinder that fits into the cuboid but if I use the cuboid and the cylinder directly it's geometrically problematic
3. ### How to calculate gating time from the rate of the random coincidence?

Hello everyone, I am now doing experiment related to quantum erasure. After plotting the correlation measurement with and without blocking one of the polarization from the SPDC source (say, V polarization), I do not know how to work further on the gating time from the rate of the random...
4. ### B Spatial Expansion -- Coincidence?

I was trying to follow how Hubble constant supposedly works. If it is about 70 km/sec/Mpc, then the the expansion at 13.8 Bly distance is about the speed of light. That, if I got it right, seems too convenient don't you think. I know it's not the same start to finish. Thanks if you can correct...
5. ### A Any electron/beta coincidence database?

Hello All, I am aware of databases which list possible gamma-gamma coincidences for desired isotope. For example: here provides a table at the bottom with all possible gamma-gamma coincidence for Co-60. Question is, are there any similar databases/tables for electron coincidences with...
6. ### I Coincidence of FLWR & CBR Homogeneity: Earth @ 0.0013c?

The Earth is moving with respect to the CBR at a speed of 390 kilometers per second, I read in the article https://www.scientificamerican.com/article/how-fast-is-the-earth-mov/. Does FLWR metric coordinate space coincides with integrated local FRs where CBR is homogeneous, and the Earth is...
7. ### I Can the quantum eraser work without coincidence?

I understand that downconverted light is not coherent, so that there are essentially many overlapping interference patterns and that coincidence detection filters out one of those patterns. However, could the downconverted light be filtered such that interference can be detected without...
8. ### B Can this be called 'a coincidence'?

Suppose we have two variables A and B. A has a truly random distribution over {0,1} with P(0)=P(1)=0.5 . B has the same distribution. Now suppose that A and B always show both a 1 or both a 0. This would be a strong correlation between A and B. Now could this be called 'a coincidence'? And if...
9. ### I Γγ Coincidence and unsuccessful linear gate method results

I had this setup (see attached photo) for the linear gate method in a γγ coincidence experiment. Using a Na22 source. The pulse from the movable detector enables the gate of the MCB, and any corresponding pulse from the fixed detector that arrives within the gate interval will be considered...
10. ### B The way the moon 'behaves', coincidence or 'something more'?

Even though the moon is much smaller than the Sun, the ratios between their distances to Earth is such that they look the same size in the sky. Further, we have a tidally locked moon with life to observe it all. Now, I'll admit this does raise some superstition in me, especially since religions...
11. ### I Circuit diagram for coincidence counting circuit

Dr Google has failed me, lots of descriptions on how its used but no circuit diagrams and how it works. Seems like a fascinating technique. Anyone got a link to a circuit diagram with explanation. Are these things available as an off the shelf black box type of deal?
12. ### I Higgs and Nuclear Yields: amusing coincidence.

I sincerely hope that the LHC people are measuring the real thing and not a leak of uranium somewhere. This is the plot of nuclear yields for spontaneous fission, extracted from wikipedia. The horizontal axis is atomic mass number and we can use 1 amu = 931.49 GeV. Some of you can remember that...
13. ### Coincidence of spacetime events & frame independence

I have been reading these notes: http://isites.harvard.edu/fs/docs/icb.topic455971.files/l10.pdf in which they claim that if two spacetime events are coincident in one frame of reference then they are coincident in all inertial frames of reference, thus spacetime events are absolute i.e. they...
14. ### Polarization coincidence formula for known polarization?

Two entangled photons from a same-polarization source have their polarization measured at 120 deg difference from each other. If I understood right all the simplified Bell-theorem and Bell-test explanations out there, QM and experiments say the chance for coincidence will be 25% no matter which...
15. ### Sun & Moon Coincidence: A Remarkable Fact

One of the things I never really thought about, but learned recently. Perhaps this is obvious to many. The relative sizes of the sun and the moon, and their relative distances from Earth make it possible for the moon to "almost" completely block out the sun during a total eclipse, allowing us to...
16. ### Coincidence Events: Understanding the Basics

Hello, I have a question about coincidence event. Let us take the decay of deuteron to proton and alpha particle, (d, pα). p and α goes in opposite direction. So, if we put two detectors in opposite directions, one of them will detect p and another will detect α simultaneously (within a small...
17. ### Gamma-gamma coincidence spectrometry

hey everyone, I know gamma-gamma coincidence detection is used to somehow determine the activity of a radioactive source, I was wondering if someone could explain to me in fairly simple terms how this is done? Also, is determining activity generally the only application for gamma-gamma...
18. ### Coincidence of asteroid and Russian meteor at same time.

Astronomers have calculated that the Russian meteor and asteroid 2012 DA14 have very different orbits: Astronomers Calculate Orbit of Chelyabinsk Meteorite. Still because of the very unlikely probability of their occurring together purely by chance, I would like to see some simulations of...
19. ### An odd coincidence or just nothing?

Hi this is my first post on this site and glad to be here! Ive only really started looking into maths and physics recently and feeling pretty overwhelmed at the moment. After reading about spacetime i was just chucking numbers around when i noticed somthing odd (to me at the time anyway)...
20. ### Pop-math book publishing coincidence

... amazing that they were published only two weeks apart (read the descriptions)! In Pursuit of the Unknown: 17 Equations That Changed the World, by Ian Stewart https://www.amazon.com/dp/0465029736/?tag=pfamazon01-20 The Universe in Zero Words: The Story of Mathematics as Told...
21. ### Interesting Coincidence with Classical/Modern View of Mass and Energy

Has anyone ever noticed that, even in classical physics, energy is shown as a scalar multiple of mass? For example, consider the joule; 1 J = 1 kg*(m/s)^2 If you consider the units of motion (m/s) to be a vector quantity, then squaring such a vector would be interpreted as a dot product...
22. ### IS this coincidence? Integral adn summation

The sum of 1 + 2 + 3...n = n(n+1) / 2 - highest power term is n^2 sum of 1^2 + 2^2 + 3^2...n^2 - n(n+1)(2n+1) / 6 - highest power term is n^3 sum of 1^3 + 2^3 + 3^3...n^3 - it has highest power term of n^4 similarly 1^k +2^k ...n^k - it has highest power term of n^(k+1) Is it a coincidence...
23. ### Calculating Gamma Coincidence Likelihood

So we know gamma decays are directionally symmetric, but assume we have two detectors and we want to know the likelihood of two γs hitting each detector at the same time as a function of the angle between the line connecting the first detector and the source and the line connecting the second...
24. ### Is this just a coincidence?

Last week, I suddenly got this drive to watch The Prince of Egypt, then I happen to stumble upon "When you believe" and got it rolling again and again. 2 days later, news came out that one of the singer were gone. Make no mistake here, I had the drive to watch the cartoon movie, not to listen...
25. ### What are some examples of coincidences in your life?

Okay, get this: A while back, while on vacation, we stopped at a outlet mall on the way home. I picked up a couple of books. After getting home, I realized that one of the books was the second in series. I went to our local large used and new book store to see if I could get the first...
26. ### Z ~ 1.6; star formation and angular diameter distance peak coincidence?

Is there any reason to expect both the star formation history and the angular diameter distance to peak at around the same value (redshift ~ 1.6)?
27. I

### Is There a Deeper Explanation for Coincidence in Physics?

Strange sequences of events seem to happen to all of us at one time or another, more specifically events that are highly unlikely to occur in the same sequence. For example, one thinks of a particular scene of a television show or movie; the individual turns on his or her TV moments later and...
28. ### Is FTL Communication Possible Through Quantum Entanglement?

Does that mean if there were zero (or close to zero) "noise" ...faster than light (flt) transfer of information would be possible? i.e. if the experiment was conducted in some dark & quite region of space-time...where only the entangled pairs were allowed strike the detectors (Ds and Dp)my...
29. ### Do we need a coincidence counter (for correlation) in delayed erasure?

Do we need a coincidence counter (for correlation) in delayed erasure?...in case of repeating the same experiment many times (with one photon at a time) the same way In the DCQE experiment such as the one listed below http://grad.physics.sunysb.edu/~amarch/ Notice the polarizer...
30. ### Did I get it right by coincidence?

Homework Statement OKay, PF again erased my hard 30mins work of LaTeX and wouldn't let me backspace. So I apologize if I miss any crucial detail Two parallel rails with negligible resistance are 10.0 cm apart and are connected by a 5.00 resistor. The circuit also contains two metal rods...
31. ### Gamma ray coincidence and multipoles

Dear Physics Forums, I am currently conducting an experiment on gamma ray coincidence from Co-60. Co-60 decays to an excited state, then de-excited by emitting two gamma rays. The aim is to deduce the angular momentum L of the first excited state. Apparently L indicates the type of...
32. ### Explaining the Speed of Light Coincidence in the Quran: A Scientific Perspective

Alright guys here's the challenge. Take this seriously because I don't understand how he got the speed of light, so is someone capable of explaining this thing step by step? My friend is a muslim, an excellent student and he claims that the speed of light is predicted in the Quran. Now he's...
33. ### Is the presence of 'c' in E=mc^2 coincidence?

Hi With special relativity I understand that if for example you have one gram of matter and it is converted to pure energy you will get E=0.001*299,792,458^2 joules of energy. However what I ‘am unsure of is; is it merely a coincidence that the value of the speed of light relates to...
34. ### Seeing 169 Everywhere: Is It Just a Coincidence?

On my 14th birthday when I bought a bike lock to go with my nifty new bike, I was somewhat surprised to see that the code for the lock was preset at 169 which was luckily enough also my house number. Well, ever since then I happen to see this number much more often than on average. It seems...
35. ### Coincidence counting in Bell experiment

I have trouble finding the following information on the coincidence counting in a Bell experiment: - Is there a fraction of single photons (not entangled) produced in the experiment and how are the final results corrected for this? - No-hits on both side can never be counted (nothing is...
36. ### Cactus Coincidence: My Friend's Cactus in Blooms & Mine Too!

Cactus coincidence! A friend of mine on another forum posted pictures of his cactus in bloom - beautiful! For those that don't own cactii, you can wait for years and years until one decides to bloom, and the blossoms are very short-lived - sometimes just a day or so...
37. ### Eliminating the coincidence counter

In DCQE, if you leave out the coincidence counter, does it effect the results at D0? Or is it impossible to know? What I want to know is...do you collapse the wave when you measure the particle...or does that information need to be accessible to a human observer. Or even simpler...in the...
38. ### Is this result by coincidence or by implication?

The other day someone gave me a puzzle. It was a geometry type puzzle but I was a able to reduce it to a set of pythagorean triads. Essentually the problem turned out to be equilvalent to the following. Find natural numbers a, b and c (each less than 42) such that {a, b, c} forms a...
39. ### Probability of a coincidence - question

Hi, I have been reading the book "200% of Nothing" by A K Dewdney, which explains various math abuses experienced in the real life. One of the examples explains the math behind a so called telepathy incidence; a coincidence in which, one gets the phone call from the very person whom she was...
40. ### Coincidence and Single Rate detection in Quantum Eraser experiments

I am having difficulty understanding why the single rate of detection (as opposed to the coincidence rate) is unaffected during Quantum Eraser experiments. I'm looking at the great Kwait, Steinberg and Chiao paper: 'Observation of a "quantum eraser": A revival of coherence in a two-photon...
41. ### Coincidence summing in gamma ray spectrometry

In gamma-ray spectrometry with germanium detector, the summing effects have to be taken into account at low source detector distance. The peaks due to coincidence summing of X+X, X+gamma, gamma+gamma rays can complicate the spectrum obtained by this type of detector and significantly change the...
42. ### Unraveling the Moon's Motion Coincidence: A Scientific Inquiry

The moon rotates on its own axis with such exquisite precision that it turns exactly once in a time exactly equal to the time to complete its orbit around Earth. How did it get that way? More - if there are plausible or proven explanations, then will the Earth day sometime end up equal to the...
43. ### Fision products, the W coincidence

Time ago I went to the NUDAT database to plot the number of known beta decays for each mass number; this is expected to reproduce the double peak curve of uranium decay, because of course more research have been done in the subproducts of this decay and then more excited, beta decaying, states...
44. S

### Is the Secret Number to the Universe 10^122?

An absurdly large number could hold the key to universal mysteries. The secret of the Universe is not 42, according to a new theory, but the unimaginably larger number 10^122. Scott Funkhouser of the Military College of South Carolina (called The Citadel) in Charleston has shown how this...
45. ### Can Three Holes in a Tall Cylinder of Water Create a Hydrodynamic Coincidence?

Given a comparatively tall cylinder full of water, is it possible to punch in its side three similar holes so that their streams all intersect at one point?
46. ### Anger of the Gods or Coincidence?

http://news.bbc.co.uk/1/hi/world/south_asia/6979292.stm Coincidence? :)
47. ### News The Unbelievable Coincidence: A Strange Tale

http://208.116.9.205/10/graphics/pics/coincidence.gif
48. ### Sun's Polar Shift on 2012 coincidence?

Ok, these are the general facts... - NASA states that the sun has gone through a polar shift on the year 2001 and will go through another one on 2012. http://www.gvnr.com/74/3.htm - For people who don't know, the Mayans had the most precise calendar of their time. The calendar states...
49. ### Your most amazing coincidence

Whether probability or luck, the psychological or psychic, scepticism or faith, physics or metaphysics, what is your greatest apparently synchronistic experience?
50. ### Another big numbers coincidence?

Have you ever thought why the ratio between the vacuum energy and dark energy, the total entropy of the observable universe and the squared ratio between the universe age and Planck time are all of them ca. 10^121, perhaps the biggest natural number with a physical significance? Any comments...